This invention relates to golf balls formed using golf ball-forming resin compositions which have flexibility and high rebound and are tough and fully wear resistant, and improved in travel distance, feel, scuff resistance and durability to repeated impact.
Polyether ester block copolymers comprising crystalline aromatic polyester units such as polybutylene terephthalate units as hard segments and aliphatic polyether units such as poly(alkylene oxide) glycols as soft segments have been of great interest as golf ball-forming resin compositions because they are flexible and highly rebound, have good mechanical properties such as strength, impact resistance and elastic recovery, and satisfactory low- and high-temperature properties, and are thermoplastic and easy to mold and work. One example is the golf ball-forming resin composition described in JP-A 7-24084.
Despite such excellent physical properties, polyether ester block copolymers are difficult to use as the cover because of shortage of scuff resistance and durability to repeated impact. Heretofore, their use has been limited to the intermediate layer of multi-piece golf balls including three- and four-piece balls. Meanwhile, ionomer resins in the form of copolymers of α-olefins and α,β-unsaturated carboxylic acids neutralized with mono- to tri-valent metal ions have long been used as the cover material, as described in JP-A 6-142228, because the ionomer resins are thermoplastic, easy to mold and work, very tough, unsusceptible to rupture even under considerable deformation at high speeds, and very advantageous in improving the scuff resistance and durability to repeated impact of golf balls.
However, these materials give a hard feel due to shortage of flexibility. It was thus proposed to use flexibilized ionomer resins in the form of copolymers of α-olefins, α,β-unsaturated carboxylic acids and α,β-unsaturated carboxylic acid esters neutralized with mono- to tri-valent metal ions, as the golf ball-forming composition. However, such flexibilized ionomer resins are inferior in rebound, low-temperature properties and scuff resistance, with further improvements being demanded.
A thermoplastic polyurethane composition made an appearance as a new cover-forming material, as described in JP-A 2004-49913. Proposed therein was a golf ball having a good balance of flight, controllability, spin stability, feel, scuff resistance and impact durability.
In this material, however, an attempt to render the material more flexible in order to improve the feel can be made at the expense of rebound and scuff resistance. Therefore, there is a desire to have a cover-forming material which takes advantage of the high rebound and soft feel of polyether ester block copolymers, and can be used to manufacture golf balls which are good in travel distance, feel, scuff resistance and durability to repeated impact; and a golf ball having a cover formed of such material.
It is noted that block copolymerized thermoplastic polyurethane elastomers obtained by reacting polyether ester block copolymers with polyisocyanate compounds are known as described in JP-A 52-121699 and JP-A 57-78413. Also, resin compositions comprising a polyether ester block copolymer in admixture with a polyisocyanate compound and a silicone compound are known to have improved wear resistance as described in JP-A 9-136934 and JP-A 10-101761.
Also known in the art are block copolymer thermoplastic polyurethane elastomers which are obtained by reacting polyether ester block copolymers with polyisocyanate compounds for the purpose of improving moldability and heat resistance (see JP-A 52-121699 and JP-A 57-78413). Also known is a composition comprising a polyester block copolymer in admixture with a specific diisocyanate compound for the purposes of improving flexural fatigue resistance and fisheyes during molding (see JP-A 2004-49913). Further known are wear resistant resin compositions comprising a polyether ester block copolymer in admixture with a polyisocyanate compound and a silicone compound (see JP-A 9-136934 and JP-A 10-101761).
All these resin compositions, however, fail to produce golf balls which satisfy the performance requirements including softness, high rebound, toughness and good wear resistance, and are improved in travel distance, feel, scuff resistance and durability to repeated impact.